This application is the national phase of international application PCT/GB99/02759 filed Aug. 19, 1999 which designated the U.S.
This invention relates to fastening arrangements, fastening methods, tools for use with said fastenings, and associated fastening kits.
1. Field of the Invention
There are many situations where it is required to connect together two items either permanently or semi-permanently and where there is access to one side only of the assembly. Examples include the attachment of panels or plates to underlying frames or supports in structures such as aircraft, ships, cars, etc. Arrangements such as captive bolts, blind rivets, rivet nuts etc., may be used in such applications. There are however disadvantages with such arrangements. For example, with rivets and captive nuts, the surface of the panel is interrupted by the head of the rivet or bolt. This interruption increases aerodynamic drag and, if the panel itself otherwise has a low radar signature, considerably increases the radar signature. In addition the exposed head of the rivet or bolt which is normally connected at its other end to a metal support structure, renders the head of the bolt or rivet susceptible to lightning strike.
2. Description of Related Art
Accordingly, there is a need for a fastener which overcomes at least some of the above disadvantages.
Thus, in one aspect, this invention provides a fastener arrangement for connecting together two members, said arrangement including:
a first component for association with a first of said members, and
a second component for association with the second of said members,
said second component including a retention element of shape memory material configurable between a closed state in which it engages first component to retain it, and an open state in which first component may be withdrawn from said second component, and a closure element adapted in use to co-operate with said retention element during fastening of said arrangement to deform said retention element from its open state to its closed state.
This arrangement therefore makes use of the recovery properties of a shape memory material to reconfigure between a closed state and an open state.
The provision of a closure element facilitates the application of an external force to deform or swage the shape memory retention element around the first component.
The first component preferably includes a head means for engaging said first member and a shank means comprising an engagement region for engaging said second component, said engagement region including a region of non-constant cross section including an abutment or shoulder region for co-operation with an associated abutment region on said retention element. In one arrangement, said region of non-constant cross section is tapered in the direction away from said head means. Many geometries are possible. In particular, it should be noted that, although in the preferred embodiment, the second component fits around the end of the first, it would be possible to have an arrangement in which the second component was deformed to fill a recess or bore within the first component.
Preferably, the retention element is made of a heat recoverable shape memory metal alloy. The retention element is preferably formed such that, when in said closed state, on heating to a temperature equal to or greater than a predetermined recovery temperature, the retention element tends to recover to said open state (assuming that the retention element is otherwise unencumbered).
To allow said retention element to be heated by the application of a coil or tool remote therefrom, the retention element is preferably made of an inductive metal material, whereby said tension element may be heated by the application of an electric field.
It will be appreciated that, in the preferred embodiment, the closure element needs to be moved into and out of engagement with the retention element to open and close it. A reasonable amount of force may need to be provided and this ideally is provided without direct mechanical application. Thus the closure element is preferably formed of a ferro-electric material whereby it may be urged into or out of engagement with said retention element by the application of an external magnetic field.
In another aspect, this invention provides a blind fastener arrangement for connecting together two members, said arrangement comprising:
a first component for connection to a first of said members,
a second component for being received in or associated with a blind recess of the other of said members,
said second component configurable between a closed state in which said first component is retained against separation from said second component and an open state in which said first component may be withdrawn from said second component,
wherein said second component is adapted to be changed between said open and closed states by the application of an electric and/or magnetic field.
Whilst the fastening arrangement defined above may be used in a wide range of different applications, it has been designed with particular reference to use for securing a first member in the form of a panel or skin element to an underlying member or structure. More particularly, the fastening arrangement may find particular application for use in connecting a panel or plate element to an underlying frame or structure. Preferably, the surface of the first member remote from said second member is substantially smooth and continuous and uninterrupted by said first component.
In another aspect there is provided a method of connecting together two members, which method comprises providing a fastening arrangement comprising a first component for association with a first of said members and a second component for association with the second of said members, said second component including a retention element of shape memory material configurable between a closed state in which engages said first component to retain it and an open state in which said first component may be withdrawn therefrom, the method comprising bringing together said two members, assembling said first component and said second component with the retention element initially in an open state, and urging a closure element against said retention element to change it to its closed state, thereby connecting said members.
Preferably the retention element is moved to its closed state by means of a closure element. Preferably, the closure element is moved between the fastened or relaxed states by means of an electrical and/or magnetic field. For release of the fastening, the retention element is preferably heated to a temperature equal to or greater than its recovery temperature. Heating may conveniently be by means of a high frequency electromagnetic field, or an electrical current.
In another aspect, this invention provides a tool for applying or releasing a fastening arrangement as defined above, including:
magnetization means for producing a magnetic field of a given polarity for urging said closure element in a direction tending to cause said retention element to change from its open state to its closed state,
magnetisation means for producing a magnetic field of a given polarity for urging said closure element in a direction out of co-operation with said retention element, and,
means for inductively and/or electrically heating said retention element.
Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description.